add bucket level S3 received/sent bytes (#15084)

adds bucket level metrics for bytes received and sent bytes on all S3 API calls.

cmd/notification.go

@@ -579,6 +579,7 @@ func (sys *NotificationSys) DeleteBucketMetadata(ctx context.Context, bucketName
 	globalBucketMetadataSys.Remove(bucketName)
 	globalBucketTargetSys.Delete(bucketName)
 	globalNotificationSys.RemoveNotification(bucketName)
+	globalBucketConnStats.delete(bucketName)
 	if localMetacacheMgr != nil {
 		localMetacacheMgr.deleteBucketCache(bucketName)
 	}